Electric motors are increasingly installed in modern motor vehicles. Said electric motors are used in this context, in particular, as drive motors which are fully integrated in the drive train or, for example, as starter generators or axle-mounted motors in hybrid applications. In this context, partially externally excited synchronous machines are used which have a rotor composed of a laminated core provided with an exciter winding. In such rotors, grooves are formed between the wound pole teeth.
During operation, high centrifugal forces, which can pull the exciter winding out of the grooves, occur both in the case of internal rotors as well as in the case of external rotors. The centrifugal forces are dependent on the rotational speed and on the weight of the groove-internal components. In particular, in the case of revving up machines the winding is therefore additionally secured after assembly. For this purpose, various bonding means are known which are used as impregnating resins or casting compounds. In addition, groove stoppers or groove wedges can be used in order to prevent the winding dropping out of the groove. Such groove wedges are known, for example, from document DE 28 17 951 A1.
In addition to externally excited synchronous machines, asynchronous machines are also installed; in particular, permanently excited synchronous machines are also used as starter generators.
So that eddy current losses which occur during operation are reduced, components of electric machines are partially fabricated from non-magnetizable materials. For example, non-magnetizable and stainless steels are used, which are also known as “Nirosta” steels (for example steel 1.4301 and 1.4303 according to the material designation according to the European standard). However, the austenitic structure of said steels is changed during shaping, punching or cutting, with the result that the steels can become magnetizable.
For many components it would also be conceivable to use plastics. However, as a rule these do not have the necessary mechanical properties to withstand high centrifugal forces.